- Add BaseTab base class for common tab initialization and logging
- Add constants module for shared GUI constants
- Move CheckboxTreeview to separate widget file
- Add admin_only and require_session decorators to utils.py
- Refactor DataExtractionTab and MaterialValidationTab to inherit BaseTab
- Remove duplicate _update_log method from tab classes
Co-Authored-By: Claude (glm-5) <noreply@anthropic.com>